(a) Field of the Invention
This invention relates to centrifugal separation of blood, namely, centrifugal batch separation of blood in a closed collapsible blood container and subsequent isolation of the centrifugally formed fractions.
(b) Prior Art
The presently predominant technique for centrifugal batch separation of blood comprises use of a collapsible main container holding whole blood to be separated and one or more initially empty auxiliary containers connected with the main container through flexible conduits.
In the most straightforward case, the blood is separated into a heavier fraction comprising the main portion of the erythrocytes (the red blood cells) of the batch of blood confined in the main container, and a lighter fraction mainly consisting of plasma. A single auxiliary container is used in this case. When the centrifugation is to be carried out, the filled main container and the auxiliary container are placed in a centrifuge in which the container assembly is centrifuged until the blood has been separated into the two fractions. Then the containers are carefully removed from the centrifuge and the plasma fraction is transferred to the auxiliary container through the connecting conduit by subjecting the main container to an exterior pressure.
Other cases may comprise separation of the blood into additional fractions, such as a fraction constituting the so-called buffy-coat, which includes the main portion of the platelets and is of a density lower than that of the erythrocyte fraction but higher than that of the plasma fraction. Consequently, upon completed centrifugation, the buffy-coat fraction, which amounts to a very small portion, one percent or so, of the total blood volume, is positioned between the plasma fraction and the erythrocyte fraction in the container. For the buffy-coat fraction a second auxiliary container is used into which that fraction is squeezed after the plasma fraction has been transferred to the first auxiliary container and the connecting conduit of the latter has been closed.
In actual practice it is very difficult or indeed impossible after the centrifugation to prevent intermixing of the fractions before the transfer into the auxiliary container or containers. When the container assembly is being lifted from the centrifuge and the main container is subjected to exterior pressure during the handling, its shape is unavoidably altered so that undesired flow within the fractions and shifting of portions of the fractions in one direction or other within the container take place, resulting in indistinct separation of the fractions. Consequently, each fraction is more or less contaminated with portions of the adjoining fraction.
Also known, but not applied in actual practice, in connection with centrifugal batch separation is a technique involving use of a single elongated blood container which is filled with a predetermined quantity of blood and then placed in a centrifuge rotor and centrifuged until the blood has been divided into two or more fractions.
In order to isolate the various fractions in the container from each other upon completion of the centrifugation, the blood container is pinched in the region of the interface of adjoining fractions, and it is also known to render the isolation achieved through the pinching permanent by welding the container walls together at the pinched region or regions. Then the blood container may be severed at the welded region or regions so that separate container sections containing different fractions are obtained.
In this case it is also virtually impossible to avoid intermixing of the fractions before they have been isolated from each other by pinching and, as the case may be, welding the container walls, because the handling during the removal of the container from the centrifuge and the pinching unavoidably result in flow within the fractions and displacement of the fractions within the container.